1. Field of the Invention
The present invention relates to compaction equipment, and more particularly to a roller of the type used in compacting surfacing materials, e.g. asphalt, for roads and the like.
2. Description of the Prior Art
In present day road building practice, when compacting certain types of road building materials, it was empirically thought that care must be taken to see that the material was not overloaded on the first pass of the roller. Hence, it was thought that the pressure exerted on the material by the first roll of the road roller to pass thereover should not exceed that overload point for the material if best results were to be obtained. At the same time, it was thought that it was desirable to approach the overload pressure as closely as possible without exceeding it, in order to compact the material to the maximum possible degree on the first pass of the roller. The overload pressure of the various materials used in the building of roads varied with the particular material being rolled, and hence it was thought to be desirable to be able to vary the pressure applied by the leading roll of the road roller so as to cause it to apply a pressure which closely approached, but did not exceed, this overload pressure of the material.
The conventional two-axle tandem road roller was not always able to meet the requirements imposed by the various types of road building materials since the load distribution on the rolls of this type of roller was fixed, usually in the ratio of 2:1, i.e. the pressure applied by the drive roll was twice the pressure applied by the guide roll. It was therefore thought to be desirable to be able to control the pressures applied by the several rolls of a road roller in various ways in order best to adapt the machine to the particular material being compacted, and to enable maximum densification of the material to be achieved by the fewest number of passes of the roller.
One proposed solution to the problem of eliminating ridges or ripples in the pavement was said to be solved by L. A. Poujard in U.S. Pat. No. 1,749,647 which used rollers mounted on an axle normally deflected with reference to a plane perpendicular to the normal path of the machine.
In the use of the conventional two-axle tandem roller, a uniform high density was achieved, but bumps caused by non-uniform thickness of the road-bed material and by unevenness of the base course, were perpetuated. It was customary, therefore, to resort to cross-rolling to reduce bumps. This was unsatisfactory inasmuch as the material had by this time set, and the lateral displacement of material which was necessary to reduce the bumps was difficult to attain. Any reduction of the bumps is done by increasing the density of the "semi-reduced" bumps which results in uneven densities in the pavement.
To overcome these problems of the two-axle tandem roller, the so-called three-axle tandem roller was devised. One such three-axle machine, shown in Greiner U.S. Pat. No. 2,015,891, dated Oct. 1, 1935, was customarily so built that, with all three rolls in contact with a plane surface, the roller approximates a two-axle tandem roller with an extra guide roll. That is, the ground reaction of each guide roll was one-half the ground reaction to the drive roll.
U.S. Pat. No. 2,132,059, issued Oct. 4, 1938, to George E. Trembly disclosed a three-axle road roller in which it was possible to adjust the relative elevations of the axles so that the rolls of the machine may be made to follow any desired road counter, that is, either a flat surface, a concave surface, or a convex surface. It was also said to be possible, in the Trembly roller, selectively to elevate either the center roll or one of the end rolls off the ground, thereby to cause different pressures to be applied by the rolls to the surface being rolled. This expedient, however, enabled only two optional pressure distributions on the rolls to be effected, neither of which could always fully satisfy the requirements of the particular material being rolled.
Canadian Pat. No. 563,757 issued Sept. 23, 1955, to John F. Harrison provided a three-axle roller in which free vertical flotation of both guide rolls was provided when desired or required, and continuous weight equalization was maintained between the two guide rolls when they were thus simultaneously released for vertical flotation. Further, either guide roll could be fixedly raised above the tangent plane of the rolls, thus providing the exact weight ratio characteristics of a conventional two-axle roller when desired, plus the characteristics of a two-axle roller in which the weight on both the drive roll and the guide roll was the same.
Canadian Pat. No. 579,559 issued July 14, 1959, to Carl F. Greiner provided a road roller having three or more rolls arranged in tandem, having a pressure control device for enabling infinitely variable pressures to be applied by the rolls to the surface being rolled, and in which one of the guide rolls was mounted for vertical displacement relative to the frame.
Canadian Pat. No. 597,717 issued May 10, 1960 to John F. Harrison provided a self-propelled road roller comprising a frame, a drive roll and a plurality of guide rolls arranged in tandem on the frame means for supporting at least one of the guide rolls for vertical displacement relative to the other rolls. Means connected between the frame and the supporting means were provided for applying a downward pressure on one guide roll in opposition to the reaction force exerted thereon by the surface being rolled. Means for adjusting the pressure applying means were provided to control the downward pressure exerted thereby on one guide roll whereby the proportion of the total weight of the roller carried by one guide roll may be selected as desired and maintained constant during rolling operations. Finally means were provided for positively limiting the upward movement of the one guide roll.
Asphalt paving machines are also known which utilize crawler-type tracks for flotation and mobility but not for compaction. Canadian Pat. No. 956,341 issued Oct. 15, 1974 to Donald R Davin et al, is one example of such machine in which the crawler track arrangement, including the track per se and the means for supporting and driving it, provided a high degree of flotation effectiveness, to prevent unduly marking previously laid pavement courses, and propelled the paving machine at adequate paving and traveling speeds.
U.S. Pat. No. 4,231,678 patented Nov. 4, 1980 by F. E. Carterrock is another example of such machine having a tracked undercarriage supporting the paving machine.
Certain facets of compaction equipment have features in common with vehicles for moving loads on difficult terrain, or for compacting soil. U.S. Pat. No. 2,714,011 issued July 26, 1955 to W. H. Albee is concerned with the former problem. That problem was said to be solved in a load moving vehicle comprising an axially elongated, flexible-walled, fluid-distensible roller for supporting the weight of a load applied to its outer surface for transportation of the load thereon. The roller included journal means of which the axis is the axis of the roller, a load-sustaining structure and removable means journaled on that structure and running upon the outer surface of the roller for applying the weight of the laod to the roller. Horizontal propulsion means were provided which had a connection to the structure and associated with the journal means for relative rotation of the two for sustaining horizontal propulsion force.
The latter problem was addressed in U.S. Pat. No. 3,603,226 patented Sept. 7, 1971 by J. Marcovitch which taught a road roller having small diameter ground engaging rolls rolling around a cylindrical backup roll located at the front of the road roller.
Another suggested solution to this problem was said to be provided in U.S. Pat. No. 3,945,748, issued Mar. 23, 1976, to Aubrey R. Berrage. In that patent, a method of soil compaction was provided by the applying, during compaction of the soil, of a smaller auxiliary force around the area of the soil to which a larger compacting force is applied. In soil compacting apparatus, a pneumatic tire was used for applying the auxiliary force and the compacting force was applied by a cylindrical or non-cylindrical compacting member located within the tire. The compacting member was adapted to compact the inner surface of the soil. A pneumatic tire, when in contact with a soil surface applied a pressure to the soil approximately equivalent to the inflation pressure of the tire. By using a "balloon" type of tire, a large area of soil was confined by the air pressure. Thus, the auxiliary force applying means may comprise a pneumatic tire. The compacting force applying means may comprise a cylindrical compacting member located inside or adjacent to the tire.